Genetics Lecture Notes Chs 13, 14, 15
Ch 13
I.
Mendel’s Laws
A.
Monohybrid cross results led to the law of segregation –
1.
Diploid cells have pairs of genes on homologous chromosomes.
2.
The two genes of a pair separate from each other during meiosis so they
end up in different gametes.
B.
Dihybrid cross results led to the law of independent assortment
1.
Paired genes on homologous chromosomes tend to sort into gametes
independently of other gene pairs during meiosis.
2.
Crossovers can breakup linkage groups
C.
Autosomal Dominant Pattern: Trait it specifies appears in everyone who
carries it – both sexes with equal frequency. Appears in every generation
D.
Autosomal Recessive Pattern: Trait it specifies appears only in
homozygous people. Equally in both sexes, but can skip generations
II.
Other Inheritance Patterns
A.
Incomplete Dominance – phenotype of heterozygous individuals is an
intermediate blend of 2 homozygous phenotypes
B.
Codominant – heterozygous individuals have both homozygous
phenotypes, may use multiple allele systems (blood typing – ABO)
C.
Epistasis – 2 or more genes affect the same trait: pigments in skin and fur
D.
Pleiotropic – gene which affects 2 or more traits: Marfan Sydrome
E.
Continuous variation – range of small increments of phenotype due to
multiple gene influences.
1.
Generally makes bell shaped curve: human height, face length in dogs
2.
Short Tandem repeats: spontaneously expand or contract quickly creating
multiple alleles (longer repeats = longer doggy faces)
F.
X-Linked Pattern – Occurs on X chromosome
1.
2.
3.
4.
Recessive pattern: X has different genetic information than Y
More often in men (XY) : Baldness
Carrier women: Dominant normal allele that masks recessive allele
Males can pass on trait to daughters but not sons
III.
External influences: Nature vs. Nurture
A.
Environmental factors can alter gene expression by way of cell signaling
pathways that ultimately affect gene controls.
B.
Change in Methylation (adding/removing methyl groups from regions of
DNA) may enhance or suppress gene expression
C.
Genotype + Environment - Phenotype
D.
Seasonal changes in coat color, altitude and plant height, reproduction and
water fleas, psychiatric disorders (ADHD)
IV.
Pedigrees
A.
Tracks inheritance patterns in families
B.
Genetic abnormality is an uncommon version of a heritable trait that does
not result in medical problems
C.
Genetic disorder is heritable condition that sooner or later results in mild or
severe medical problems
D.
Used for to visualize inheritance patterns that can be predictably
associated with specific phenotypes
V.
Chromosomal Number
A.
Karyotypes are pictures of total numbers of chromosomes in an individual
B.
Aneuploid individuals have too many or too few copies of a chromosome
C.
In humans, most are lethal <1% individuals
D.
Nondisjunction occurs during meiosis due to faulty separating of
chromosomes or chromatids in Anaphase 1 or 2.
E.
EX: Downs syndrome (trisomy 21), Changes in #s of sex chromosomes
VI.
Chromosomal Structure
A.
During Prophase I, faulty crossovers can result in abnormal chromosomal
structure
B.
Changes can be harmful or lethal. Some affect fertility – ½ of all
miscarriages are due to chromosome abnormalities
C.
Changes have accumulated in chromosomes of all species over time
1.
Telomere section found in middle of Chromosome 2 of humans suspected
fusing of 2 chromosomes (2A and 2B in chimpanzees)
D.
X and Y chromosomes were once homologous autosomes in reptilelike
ancestors of mammals.
1.
SRY gene mutated resulting in reduced crossing over – allowing
chromosomes to diverge and mutations accumulate separately
VII. DNA Cloning
A.
Restriction enzymes are used to cut a sample of DNA into pieces.
B.
DNA ligase splices the fragments into plasmids (circular pieces of DNA from
bacteria).
C.
New recombinant DNA are inserted into host cells like bacteria
D.
Division of host cells produces huge populations of genetically identical
cells – clones – each containing the DNA fragment
E.
Reverse transcriptase is used to transcribe RNA into cDNA for cloning
VIII. Genetic engineering
A.
Scientists use a DNA library containing different fragments of DNA to
represent an organism’s entire genome.
B.
PCR uses primers to rapidly increase number of copies of a targeted section
of DNA without needing to clone living cells
C.
Electrophoresis – separates fragments of DNA cut by restriction by length
into bands
D.
Sequencing reveals the order of nucleotides in DNA
E.
Human genome project has sequenced the entirety of the human genome
(3 billion nucleotides)
F.
Genomics provides insights into the function of the human genome.
1.
Looks for similarities between different organisms for evidence of
evolutionary relationships
G.
DNA profiling can identify a person by SNPs (single nucleotide
polymorphisms) which is an array of short tandem repeats : DNA fingerprint
H.
Taking one gene from one species and inserting it into an individual of a
different species OR modifying it and inserting it into the same species creates
GMOs.
1.
2.
value
Bacteria and yeast produce proteins with medical value
Transgenic crops: corn and soy: pesticide resistant/increased nutritional
I.
Gene therapy transfers a gene into body cells to correct a genetic defect or
treat disease
1.
Potential benefits weigh against risks like eugenics